Air quality degradation in Alaska wilderness areas due to emission changes

Abstract

The increasing trends in aerosol concentrations observed by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network in the wilderness areas along the Gulf of Alaska during low insolation periods and in Denali National Park and Preserve (Denali NP) during high insolation periods have raised the concerns about air quality degradation and visibility impairment in these pristine areas. This dissertation aims to investigate the reason for those observed increases in aerosol concentrations in Alaska wilderness areas by performing a series of simulation sets with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). These simulation sets use the same meteorological conditions but change the emission scenarios. The model evaluation analysis showed that WRF-Chem performed well in simulating meteorological conditions over Alaska and the North Pacific under both low and high insolation conditions. Performance skill-scores of the WRF-Chem model in simulating aerosol concentrations for the coastal monitoring sites along the Gulf of Alaska were consistent with state-of-the-science air-quality model performance. During low insolation periods, domestic and international ship emissions were the most important contributors to aerosol concentrations in the coastal regions along the Gulf of Alaska. The increases/decreases in ship emissions led to subsequent increases/decreases in aerosol concentrations in the coastal areas along the Gulf of Alaska during low insolation periods. During high insolation periods, in Interior Alaska, the contributions of local wildfire emissions to aerosol concentrations were notable even during the weak Alaska fire activity scenario. Under the strong Alaska fire activity scenario, local wildfire emissions were the dominant source of aerosols in Interior Alaska. The increases in Alaskan wildfire emissions led to significant increases in aerosol concentrations in Interior Alaska. During both low and high insolation periods, Japanese anthropogenic and Siberian wildfire emissions were not important contributors to total aerosol concentrations in all regions of Alaska. Overall in the wilderness areas along the Gulf of Alaska, the increases in aerosol concentrations observed during low insolation periods stemmed from increases in domestic and international ship emissions in the North Pacific. In contrast, the increases in aerosol concentrations observed at Denali NP during high insolation periods stemmed from increases in Alaskan wildfire emissions.